Turbine and compressor assemblies for a gas turbine engine includes a plurality of turbine blades mounted on a generally annular rotor disc so as to protrude radially therefrom. Each blade includes an aerofoil portion, which projects into the path of gases flowing axially through the turbine and compressor, and a root portion which is attached to the rotor disc. Commonly, the blade includes a “firtree” root portion which has as undulating profile and is designed to slide into a complementary recess provided at the surface of the rotor disc.
Turbines and, to a lesser extent compressors, are required to operate at extremely high temperatures and therefore the material of the blades and the disc must be able to withstand such temperatures. A failure of a blade or, even more seriously, of a disc can be extremely serious. The discs are therefore made from materials which are highly heat resistant, resistant to corrosion from cooling air and have very good tensile properties. High strength nickel alloys are commonly used materials.